Pipe forming



June 22, 1965 WILSON, JR 3,189,992

PIPE FORMING Filed June 7. 1961 INVENTOR. JOHN L. WILSON JR.

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ATTORNEY.

United States Patent 3,189,992 FIFE T GER ENG John L. Wilson, In, Pittsburgh, Pa., assignor to Salas Corporation of America, Brasher, 1 22., a corporation of Pennsylvania Filed June 7, 1961, Ser. No. 115,486 2 Claims. (Cl. 29-47737) The present invention relates to tube forming, and more particularly to a method to be used in the manufacture of continuous butt or fusion welding pipe and tubing.

Ordinarily in the forming of pipe or tubing of this type, flat skelp is heated and bent to a tubular shape. Thereafter the edges of the skelp are heated to fusion temperature and forced together to make the pipe. This procedure has several disadvantages, including the difiiculty of threading the skelp through the furnace, as well as the requirement of special strip handling rollers. If the skelp is bent into substantially tubular form prior to the time it is heated, it is difficult to heat the material evenly and rapidly throughout its area prior to the final heating and closing steps.

It is an object of the invention to provide a method of forming pipe from skelp, which will permit individual lengths of skelp to be readily handled and heated.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings:

FIG. 1 is a diagram of apparatus by means of which the method can be carried out,

FIG. 2 is a section through the preformed skelp taken on line 2-2 of FIG. 1, and

FIG. 3 is a section through a furnace taken on line 3-3 of FIG. 1.

In general, the method is practiced by moving lengths of skelp cold formed to U-shape on a conveyor through a preheating furnace consisting of a plurality of barrel furnace units 1. From this furnace the skelp goes through a set of forming rolls 2 which move the edges closely adjacent to each other prior to the time they are heated to fusion temperature bq jetburners 3. The tube blank is then moved through a set of rollers 5 that move the edges together to close the seam and form a tube or pipe. A welding torch 4 may be used at this point if desired or necessary. The tube is then moved into a reheating furnace comprising a plurality of barrel furnace units 6, where its temperature is equalized throughout its area, and it is brought up to hot working temperature. From here the tube immediately passes to a stretch mill 7 which reduces the tube to the diameter of the particular size required at the time. The pipe can then be cut in any conventional manner to the required lengths.

Ordinarily skelp that is to be used for tube or pipe making is supplied fiat from rolls to the preheating furnace. This means that the trailing end of one roll must be attached to the lead and of the next for a continuous process. If, for some reason, the process is shut down, the strip 'in the furnace will be burned. Rethreading is a difiicult and time consuming procedure, because the strip is not self-supporting as it is moved from one forwarding roll to the next through the furnace. Occasionally the skelp is preformed to bring the edges close together to substantially tubular shape prior to the time preheating takes place. Such a procedure requires a relatively long time to heat the blank, because the metal can be heated only from the outside. In addition, some means is required to guide the blank so that the cleft between the edges remains accurately in the proper position.

In accordance with the present invention, the skelp is cold formed in convenient lengths to an are that is great enough to give the strip sufficient rigidity to support itself between spaced conveying rollers. The strip, however, is open enough so that it can readily be heated from both sides. Referring to FIG. 2, it will be seen that the skelp 11 has been cold formed to an are that is more than but still has its edges far enough apart so that heat can be directed to the interior as well as around the exterior of the form. Ordinarily the arc will be between 180 and 270. As shown in the drawing, the portions of the skelp adjacent to the edges are bent to the final tube radius, while the lower part of the skelp is bent on a larger radius. This is a matter of convenience rather than being essential to the invention, since, as far as the invention is concerned, the radius could be uniform from edge to edge. In the subsequent forming of the pipe by moving the edges together, it is sometimes easier to have the edges initially bent to the final pipe radius. This type of bending, however, apparently produces a slightly more rigid formed part to be forwarded through the furnace. By bending the skelp at least 180 it will have enough rigidity when it is heated to be moved from one conveying roller to the next as it is traveling through the units 1 forming the preheating furnace. In addition, skelp bent to the form shown will remain in position on the conveying rolls without the necessity for additional guides.

The cold formed skelp 11, that may be in lengths from about 30 to over 100, is placed on conveyor rolls 12 of hour-glass shape having a curve approximating that of the skelp. These rolls are mounted on shafts 13, that may be water cooled, and which are driven to move the skelp through the above described path.

As the preformed skelp 11 is moved through the units of furnace 1, it is brought up to a temperature of about 1600 F. to G F. Each of the furnace units is generally cylindrical in shape, and has axially disposed openings in each end through which the skelp travels. Referring to FIG. 3, each furnace unit 1 is shown as being constructed of refractory material 14 to form a cylindrical furnace chamber 15 having an opening 16 in each end. The unit is mounted on supports 17 so that the openings 16 are axially aligned with skelp moving on the conveying rolls 12. Each unit is provided with at least four burners 18. These burners are preferably and are shown as being of the radiant cup type such as those disclosed in Furczyk Patent No. 2,855,033.

Such burners are provided with a cup-shaped depression 19 into which a plurality of streams of a combustible mixture are discharged by a centrally located. fuel distributor 21. The fuel mixture burns along the surface of the cup to heat it to incandescence, so that radiant heat of high intensity is directed from the cup toward the Work. Heating is also produced by the hot products of combustion released in the furnace.

The lower burners 18 are so located in the furnace that the radiant heat rays are directed against the lower outside surface of the skeip. The upper burners are so located that some of their direct radiant heat strikes the upper outside portions of the skelp. A large portion of the direct heat from these burners, however, is directed into the interior of the skelp form to heat the interior directly. This is possible because of the fact that there is a large distance between the upper edges of the skelp. In addition, the wide opening between the edges of the skelp permit free circulation of hot gases over the entire surface of the material, thus increasing the speed at which it is heated.

The burners are supplied either with separate supplies of fuel and air or with a combustible mixture from a suit .2- able mixing machine through pipes shown diagrammatically at 22. A regulating valve 23 is in the line to each burner, and all of the burners of a furnace unit or group of furnace units can be regulated by a conventional tem- 7 perature regulator.

When the preformed and preheated skelp leaves the furnace units 1, it goes through a set of forming rolls 2 that move the edges of the skelp closely together to form a narrow cleft between them. The slaelp, now substantially tubular in shape, is next moved below burners 3 that preferably are of the type shown in Furczyk Patent No. 2,561,194. These burners direct a hot, high velocity stream of products of combustion against the edges of the shape to heat them to a temperature approaching the melting point of the metal, or about 2450" F. Since the heating is done by hot products of combustion that are nonoxidizing in character, and which blanket the work, substantially no oxidizing takes place even at the high temperatures achieved.

When the tube leaves the edge heating burners, it moves between a set of closing rolls 5. If desired, a torch 4 can be used to melt the edges before they are moved together. At this point in the path of travel, the edges of the skelp are forced together to close the seam and form the tube or pipe. When the tube is formed, its temperature must be equalized throughout to relieve the Welding strains. 1 f the tube is to go through a stretch mill, it must also be heated to hot working temperature. Therefore, as the tube leaves forming rolls 5, it is fed into a reheating and equalizing furnace comprised of a number of barrel furnace units 6 similar to furnace units 1. These furnace units equalize the temperature of the tube and brings it up to approximately 1850 F. From the reheating furnace the tube goes into stretch mill 7 where it is treated conventionally to reduce its diameter and increase its length.

In summary, and as a specific example of the method, skelp in convenient lengths of 17" width and thickness is cold formed to an arc of about 270. This will leave a gap between the edges of about 6 /2". Such shape has sufficient strength to remain rigid as the skelp is moved endwise into and through the furnace units, even when the conveyor rolls are 7 or 8 feet apart. The skelp is fed into preheating furnace units 1 at room temperature and discharged at a temperature of about 1850 F. At th s temperature forming rolls 2 will move the edges within /2" of each other, sothat the blast of hot gases from burners 3 can heat the edges simultaneously to about 2450 F. The heated edges will then be continuously moved together in a butt weld to form a tube by roll stand 5.

During the time that the skelp and tube are moving from furnace 1 to the exit of roll stand 5, the body of the tube has cooled somewhat, while the Welded seam is still almost at its final temperature. If desired, the seam can be cooled somewhat by a jet of cooling fluid before the tube passes into the equalizing furnace 6. This latter 7 furnace serves not only to equalize the temperature of the tube, but also to raise its temperature to about 1900 F. before it goes into the stretch mill 7 for final sizing. After leaving the stretch mill, the tube is cut by any conventional means into lengths for use.

The speed at which the skelp is moved through the various pieces of apparatus along its path is determined solely by the number of furnace units in the various furnaces and the stretch mill. The speed of the entering skelp will ordinarily Vary between 150' and 260 per minute, with the exit speed from the stretch mill going as high as 2000 feet per minute when very small diameter pipe is being made.

An advantage of the present method is that the same apparatus used for handling the preformed skelp can be used for heatingelectric Welded pipe before supplying it to the stretch mill. Since the prefeormed pipe has an arcuate shape, it is handled and moved through the furnaces on hour-glass rolls, rather than cylindrical rolls that would be used in conventional skelp furnaces. These same hour-glass rolls will properly support electrically welded pipe as it is being heated prior to stretching.

While in accordance with the provisions of the statutes,

1 have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is: 1. The method of forming pipe or the like from skelp which comprises cold forming the skelp transversely into an arc of from to 270 with the edges spaced from each other, moving the skelp continuously through a path in an axial direction with the edges facing in an upward direction, at a first portion of said path heating said formed skelp to above 1600 F. predominantly by radiant heat directed toward the outside and through the space between said edges directed toward the interior of said formed skelp, moving said edges closely adjacent to each other, at another portion of said path heating said edges with hot, non-oxidizing products of combustion that blanhot the formed skelp,

moving the heated edges together to Weld them to each other thus forming a pipe, and

at another portion of said path heating the entire pipe to a degree to equalize its temperature and relieve the welding strains. 2. The method of forming a pipe or the like from skelp which comprises cold forming lengths of skelp transversely into an arc of from 180 to 270 with the'edges parallel and separated,

moving the formed skelp continuously in an axial direction through a path with said edges directed upwardly and performing operations thereon in sequence comprising heating the formed skelp predominantly by radiant heat directed against the outside and against the inside of said formed skelp between the edges thereof,

moving said edges closely adjacent to each other,

heating said edges to a temperature approaching the melting point of the skelp by a hot blast of nonoxidizing products of combustion, which products of combustion blanket the formed skelp,

moving said edges together to form a pipe, and

heating said pipe throughout to equalize the temperature thereof and relieve the welding strains.

References Cited by the Examiner UNITED STATES PATENTS 1,893,926 1/33 Anderson 11333 2,197,962 4/40 Anderson 78-83 2,581,673 1/52 (ennedy 1l3-33 Heussner 113-33 CHARLES W. LANE-1AM, Primary Examiner.

NEDWIN BERGER, WILLIAM J. STEPHENSON,

Examiners. 

1. THE METHOD OF FORMING PIPE OR THE LIKE FROM SKELP WHICH COMPRISES COLD FORMING THE SKELP TRANSVERSELY INTO AN ARC OF FROM 180* TO 270* WITH THE EDGES SPACED FROM EACH OTHER, MOVING THE SKELP CONTINUOUSLY THROUGH A PATH IN AN AXIAL DIRECTION WITH THE EDGES FACING IN AN UPWARD DIRECTION, AT A FIRST PORTION OF SAID PATH HEATING SAID FORMED SKELP TO ABOVE 1600*F. PREDOMINANTLY BY RADIANT HEAT DIRECTED TOWARD THE OUTSIDE AND THROUGH THE SPACE BETWEEN SAID EDGES DIRECTED TOWARD THE INTERIOR OF SAID FORMED SKELP, MOVING SAID EDGES CLOSELY ADJACENT TO EACH OTHER, AT ANOTHER PORTION OF SAID PATH HEATING SAID EDGES WITH HOT, NON-OXIDIZING PRODUCTS OF COMBUSTION THAT BLANKET THE FORMED SKELP, MOVING THE HEATED EDGES TOGETHER TO WELD THEM TO EACH OTHER THUS FORMING A PIPE, AND AT ANOTHER PORTION OF SAID PATH HEATING THE ENTIRE PIPE TO A DEGREE TO EQUALIZE ITS TEMPERATURE AND RELIEVE THE WELDING STRAINS. 